We wish to study in the organ or Corti of the mouse the interrelations between the hair cell and the spiral ganglion fibers innervating it when the entire system has been excised from the organism and develops in vitro. Morphological observations will be made using light microscopy for the study of the live tissue; the light and electron microscopes will be used for the studies of fixed material. The results obtained on cultured material will be compared whenever applicable with the findings in the developing intact mouse. The three projects of immediate interest are: 1) Development of synaptic ribbons and afferent synapses in the organ of Corti in culture, 2) Ultrastructural study of developmental sequence in formation of afferent synapses, 3) Development of the afferent innervation in the organ of Corti of the Bronx Valtzer mutant in culture.